Interaction of photoswitchable nanoparticles with cellulosic materials for anticounterfeiting and authentication security documents.

Invisible high-security anticounterfeiting inks were developed by surface-modification of functionalized latex nanoparticles with spiropyran derivatives, which display both photochromism and fluorescence upon UV irradiation at the same time. The functionalized latex nanoparticles show different spherical, doughnut-like, and red blood cell-like morphologies depending on concentration and type of its functional groups. Microscopic investigation of the impregnated cellulosic papers with latex nanoparticles display that epoxy-functionalized spherical latex nanoparticles have considerable packing and stability on the surface of the cellulosic substrate by formation of hydrogen bonding. Epoxy-functionalized latex nanoparticles containing spiropyran were used for preparation of high-security photochromic/fluorescent anticounterfeiting inks for print-marking of different cellulosic security documents such as certificate, money, and passport with different marks. The printed marks and finger-prints on the cellulosic security documents display photochromism and red fluorescence emission upon UV irradiation with high intensity and brightness.